Method for limiting battery discharging current in battery charger and discharger circuit

ABSTRACT

A power supply system includes a rechargeable battery to deliver a supply current to a load and a circuit to limit a discharge current when the rechargeable battery is supplying power to the load. The power supply system may further include an integrator for integrating a discharge voltage representing the discharge current that exceeds a predetermined limit, a pulse-width-modulation (PWM) circuit for producing a control signal having a PWM duty cycle representing the discharge voltage, and a driver circuit for delivering the supply current to said load according to said control signal. In one embodiment, a digital register is used to set the battery discharging current limit, in another embodiment an analog circuit is used to set the battery discharging current limit, and in yet another embodiment or a combination of the digital register and analog circuit is used to set the battery discharging current limit.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/418,616, filed Dec. 1, 2010, and also claims thebenefit of U.S. Provisional Patent Application Ser. No. 61/479,284,filed Apr. 26, 2011, both of which are assigned to the assignee hereofand incorporated herein by reference in their entireties.

FIELD

The various embodiments described herein relate in general to hybridpower supply circuits, and the like, and methods for controlling same,and more specifically to methods and circuits for controlling thecurrent drawn from a battery associated with the hybrid power supplycircuit in a mode in which supply current is needed in excess of thatwhich can be supplied by a power supply adapter.

BACKGROUND

Rechargeable batteries, typically lithium-ion batteries, are widely usedin consumer electronic devices, especially portable computers and mobiledevices. Although examples of devices with which such batteries may beused are manifold, some recent examples include smartphone, notebook,tablet, and netbook computing devices, or the like, which have a CPU andmemory that require operating power. When the device is not powered bythe battery, an adapter is commonly used to power the device with whichthe battery is associated. At the same time, the adapter provides powerto a charging circuit in the device to charge the battery. In suchcharging circuits, a synchronous switching buck converter is often usedto control the charging current to the battery, while providing asubstantially constant voltage to the load.

Traditionally, when the power required by the CPU and system loadincrease to reach the adapter power limit, the charge current can bereduced to zero, thereby giving a higher priority to power the systemthan to charge the battery. However, in certain conditions, if the CPUpower demands are greater than those that can be met by the adapter, theadapter may crash. An example of such condition is when the system iscold and the CPU power needed for application processing and speeding updata flow is much more than the power that the adapter can supply, evenwith zero charging current.

In the past, several solutions to the problem have been advanced. Forexample, one solution disables the CPU high current mode. This, however,lowers the system performance. Another solution uses an adapter with anincreased current capability. This, however, increase the adapter cost.Yet another solution reduces the system bus voltage. This, however, isnot a widely adopted battery charger solution, and is not suitable for ahigh power system. Still another solution is to add an additional boostconverter and include a boost controller. This, however, requires atleast a power MOSFET, diode, and other circuit components. The cost ofthis solution is high and needs more space.

Thus, in order to solve the problem of operating a CPU at a high speedto improve the system performance, while not crashing the adapter, ithas been suggested to use the battery and adapter to simultaneouslypower the system when power demands are high. One way in which this hasbeen done has been to use a boost converter in the charging circuit toconvert the battery power for delivery to the system. The charger canoperate in a synchronous buck mode during the battery charging and in aboost mode when additional power to CPU and system is needed. This typeof charging circuit is referred to herein as a “hybrid power batterycharger.”

Because the adapter current is well controlled by the hybrid powerbattery charger, the battery discharging current changes when totalsystem current changes. However, for any particular portable device,numerous battery pack options may be available. For example, numerousinterchangeable battery pack designs may be used. For example, 3S1P (3cells in series 1 cell in parallel), 3S2P, 3S3P, and so on can be usedto power the same device. However, different battery packs havedifferent discharging current capabilities. Thus, for the same device,different power delivery capabilities may be available, depending on theparticular battery pack design that is selected or installed.

Each battery pack generally has an over-current protection circuit toprotect the battery in the event the load attempts to draw current abovea maximum current level that is established for the battery. Forexample, usually, the over-current protection circuits turn off abuilt-in MOSFET device in series with the battery output, if the currentdrawn from the battery is over the maximum current level. In normaloperation, it is preferred that this kind of protection should never betriggered.

What is needed, therefore, is a system and method of the type that usesthe battery charger in a boost mode to boost the current available fromthe battery to supplement the adapter current when needed, and thatcontrols the discharge rate of the battery when it is connected in thismode.

SUMMARY

This various embodiments described herein use a digital register to setthe battery discharging current limit, an analog circuit to set thebattery discharging current limit, or a combination of the two previousmentioned methods to set the battery discharging current limit. Acurrent sensing resistor and differential amplifier sensing thedischarging current along with the closed current control loop regulatethe discharging current to a level no more than the discharging currentlimit set by either from digital register or analog circuit.

Thus, in accordance with one embodiment disclosed herein, a power supplysystem is described which includes a rechargeable battery connectable todeliver a supply current to a load and a circuit to limit a dischargecurrent when the rechargeable battery is supplying power to the load.The power supply system may further include an integrator forintegrating a discharge voltage representing the discharge current thatexceeds a predetermined limit, a pulse-width-modulation (PWM) circuitfor producing a control signal having a PWM duty cycle representing thedischarge voltage, and a driver circuit for delivering the supplycurrent to said load according to said control signal.

According to a method embodiment a method for operating a power supplysystem is described in which a rechargeable battery is provided that isconnectable to deliver a supply current to a load, and a circuit isprovided to limit a discharge current from the rechargeable battery whenthe rechargeable battery is supplying power to the load. The method alsoincludes switching from a buck mode of operation to a boost mode ofoperation in which the rechargeable battery supplies additional supplycurrent to the load. When the discharge current exceeds a predeterminedlimit, a control signal is generated having a duty cycle correspondingto an amount by which the discharge current exceeds the predeterminedlimit, and the control signal is used to control the supply current tolimit the discharge current.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example of a hybrid battery chargerenvironment in which battery charging and controlling circuits andmethods described herein may be employed.

FIG. 2 is an electrical schematic diagram illustrating an example of anembodiment of a charger circuit having a voltage boost function that maybe used in the battery charging and controlling circuits and methodsdescribed herein.

FIG. 3A is a block diagram of an example of feedback amplifier,integrator, duty cycle, and driver circuits for implementing the batterycharging and controlling circuits and methods of FIG. 2.

FIG. 3B is a block diagram of an example of start/stop boost modecontrol circuits for implementing the battery charging and controllingcircuits and methods of FIG. 2.

FIG. 4 is an electrical schematic diagram of one embodiment of aprogrammable circuit for regulating the discharge current of arechargeable battery pack, using a digital register to enable thedischarging current limit to be set by a host, such as a smartphone,notebook, tablet, netbook computing device, or the like.

FIG. 5 is an electrical schematic diagram of another embodiment of aprogrammable circuit for regulating the discharge current of arechargeable battery pack, using a hardware pin voltage that may be setby a user.

FIG. 6 is an electrical schematic diagram of yet another embodiment of aprogrammable circuit for regulating the discharge current of arechargeable battery pack, using both a digital register and a hardwarepin voltage to enable the discharging current limit to be set by a hostor by a user.

In the various figures of the drawing, like reference numbers are usedto denote like or similar parts.

DETAILED DESCRIPTION

A block diagram of an example of a hybrid battery charger environment 10is shown in FIG. 1. The hybrid battery charger environment 10 includes asystem 12, which may be, for instance, a smartphone, notebook, tablet,netbook computing devices, or the like, which has a CPU 14 and a memory16 that require operating power. The CPU 14 and memory 16 are part ofthe system load 18 for which the operating power is needed. Theoperating power to the system load is provided by a buck/boost chargersystem 20 and an associated rechargeable battery pack 22, in a mannerdescribed below in greater detail. The rechargeable battery pack 22 maybe a lithium-ion battery pack, for example, although other rechargeablebattery types may also be employed.

An adapter 24 is provided, which is optionally connectable to receive acpower, typically from an ac outlet, not shown, to convert the ac powerto dc power to supply power to the buck/boost charger system 20 to powerthe system load 18, and to charge an associated rechargeable batterypack 22. For example, depending on the particular power requirements ofa particular system load 18, a typical adapter may supply 90 W of powerat about 20 V, thereby having the capability of supplying about 4.5 Acurrent. The adapters, of course are load dependent, and may varygreatly from one application to another; however, one of the advantagesof the hybrid battery charger of the type described herein is that thepower requirements of the particular adapter needed can be reduced fromthat which would be required if the adapter alone is used to supplyoperating power to the system load 18. The adapter 24 may be supplied asa component that is external to the device or system that it is intendedto supply power, and is selectively connectable thereto.

A switch 26 connects the battery pack 22 to the system load 18 when theadapter 24 is not connected to receive ac power so that system load 18is powered by the rechargeable battery pack 22 directly. When theadapter 24 is connected to receive ac power, switch 26 is opened todisconnect the rechargeable battery pack 22 from system load 18 so thatsystem load 18 is powered by the ac adapter directly. According to theembodiments described below, the rechargeable battery pack 22 can supplyadditional power to the system load 18 when the capabilities of theadapter 24 are exceeded. More specifically, when the power required bythe system load 18 is more than the adapter 24 can provide, thebuck/boost charger system 20 may call upon the rechargeable battery pack22 to provide the additional power, for example by switching therechargeable battery pack 22 into the system by, for instance, changingthe buck converter charger to a boost converter. In addition, when thepower required by the system load 18 is higher than that which can beprovided by the adapter 24, the battery charge current is not onlyreduced to zero, but the buck/boost charger system 20 is operated in aboost mode so that the adapter and battery power the systemsimultaneously.

In one embodiment, if the power demanded by the system load 18 reachesan overload condition of the adapter 24 at or exceeding the maximumpower limit of the adapter, the buck/boost charger system 20 changesfrom buck mode to boost mode and allows the rechargeable battery pack 22to provide additional power to the system load 18. As a result, theadapter 24 and the rechargeable battery pack 22 together providesufficient system power, thereby avoiding an adapter crash and enablingthe system load 18, including its CPU 14, to receive maximum availablepower for achieving its highest performance.

With reference now additionally to FIG. 2, an electrical schematicdiagram is shown, illustrating an example of an embodiment of a chargercircuit 30 having a voltage boost function that may be used to providethe battery charging and controlling circuits and methods describedherein. The charger circuit 30 has a dynamic power management (DPM)circuit 32 that receives input power on input node 34 from an adapter 24of the type described above which can be selectively connected thereto.

The DPM loop 32 includes an input current sensing resistor 36, the nodeson either side of which being designated “ACP” and “ACN,” which areconnected as inputs to the charger control loops 38, described below ingreater detail. A pair of MOSFET devices 40 and 42 are connected toreceive respective high-side and low-side driving voltages from thecharger control loops 38, depending on whether the charger is operatingin buck or boost modes. An inductor 44 is connected to the rechargeablebattery pack 22 by a charge current sensing resistor 46. The respectivesides of the charge current sensing resistor 46 are designated “SRP and“SRN,” and are connected as inputs to the charger control loops 38, asdescribed in greater detail below. The power output from the chargercircuit 30 is represented by the VBUS voltage shown between line 48 andthe reference potential, or ground line 50, and by the current sourceI_(SYS) 52.

With reference now additionally to FIG. 3A in which is shown theamplifier 60, feedback integrator 66, duty cycle, and driver circuits62, and to FIG. 3B in which is shown the boost stop and start circuit64. The amplifier circuits 60 receives inputs ACP, ACN, SRP, and SRN,respectively, from the input current sensing resistor 36 and chargecurrent sensing resistor 46, providing an input to the type IIIcompensation circuit 66. The output from the compensation circuit 66 isapplied to a control loop saturation determining circuit 68 and to a PWMcircuit 70. The output from the control loop saturation determiningcircuit 68 is connected to the boost stop and start circuit 64,described below, and the output from the PWM circuit 70 is connected tothe driver logic circuit 72.

The start boost and stop boost signals developed in the boost stop andstart circuit 64 are also connected as inputs to the driver logiccircuit 72. The outputs HSON and LSON signals are connected to outputdrivers 74 and 76, which are level adjusted by BTST, PHASE and REGN andGND voltages to provide drive signals to the MOSFET devices 40 and 42(FIG. 1) at the correct voltage levels.

The boost start and stop circuit 64 is shown in FIG. 3B, to whichreference is now additionally made. The boost start and stop circuit 64receives inputs representing the voltage difference between ACP and ACN.This voltage difference may be developed, for example, in the amplifiercircuits 60 of FIG. 3A, with appropriate scaling.

With respect to the start boost mode, the voltage difference between ACPand ACN is compared to a reference voltage, for example 1.05 X VREF_IACby comparator 80. VREF_IAC represents a particular upper current levelthat is established by the host below which operation of the adaptershould be held to avoid crashing the adapter. The comparator 80 hashysteresis so that momentary changes in the ACP-ACN voltage differencedo not cause the comparator 80 to revert to its previous state. Thereference voltage is established such that if the voltage differenceACP-ACN developed across the input current sensing resistor 36 reaches apredetermined percentage of the power limit of the adapter 24, in thiscase 105%, the comparator 80 changes output state.

In the particular embodiment illustrated, the output from the comparator80 is connected to a delay circuit 82 which operates to shut down thecharger and begin a predetermined delay, for example 170 μs in responseto the change of state in the output of the comparator 80. If thevoltage output from the comparator 80 returns to a low value before thepredetermined delay, indicating that the boost mode is not required, theboost mode is not initiated and the charger is turned back on. However,after the expiration of the predetermined delay, the start boost outputchanges state, triggering the driver logic circuit 72 (FIG. 3A) to turnon the low-side MOSFET device 42 (FIG. 2) via the low-side driver 76 andhigh-side MOSFET device 40 (FIG. 2) via the high-side driver 74.

With respect to the stop boost signal, four possible input signals cantrigger the stop boost signal. The four signals are applied to an ORgate 83, the output of which being the stop boost signal that is appliedto the driver logic circuit 72 (FIG. 3A). The first input signal is animmediate trigger developed by comparator 84 when the voltage differenceACP-ACN is less than a predetermined voltage, such as 10 mV. When thiscondition occurs, the boost mode is immediately shut down to preventACOV (system bus over voltage). The second input signal is a triggerthat occurs when the voltage difference ACP-ACN is a predeterminedpercentage below the VREF_IAC voltage level. In the example illustrated,the percentage is 93%, and is established by the comparator 86. If thevoltage difference ACP-ACN is a predetermined percentage below theVREF_IAC voltage level, and the output from the comparator 84 is nothigh, a 1 ms delay is timed by a timer 88 to trigger the stop boostoutput signal.

In addition, if the control loop is in saturation, determined in block90, and if the voltage difference ACP-ACN is not a predeterminedpercentage below the VREF_IAC voltage level, the stop boost outputsignal is triggered. Finally, a watchdog timer 92 is provided to assurethat the boost mode does not remain engage for a predetermined time,such as 175 seconds in the example shown.

When the charger circuit 30 is in boost mode, the discharge current ofthe rechargeable battery pack 22 may be regulated by a rechargeablebattery pack current regulation circuit. One embodiment of arechargeable battery pack current regulation circuit 100 that may beemployed is shown in FIG. 4, to which reference is now additionallymade. The battery pack current regulation circuit 100 of FIG. 4 isprogrammable through the use of a digital register 102 that enables thedischarge current limit to be set by a host 101, such as a smartphone,notebook, tablet, netbook computing device, or the like, via a systemmanagement bus, an I2C bus, or the like. The host 101 may include thesystem load 18 (see FIG. 1), for example, and, in some embodiments, mayalso carry the rechargeable battery pack 22.

In operation, the battery pack current regulation circuit 100 senses thedischarge current from the rechargeable battery pack 22 by monitoringthe voltage nodes SRP and SRN on each side of the charging currentsensing resistor 46 (see FIG. 2). In FIG. 4, the current in the chargingcurrent sensing resistor 46 is labeled “I_(DISCHG),” since the dischargecurrent is of interest when the charger circuit 30 is in its boost modeof operation and the rechargeable battery pack 22 is used to supplementthe current from the adapter 24 and is therefore discharging current.

The voltage on the nodes SRP and SRN is applied to the inputs of anoperational amplifier 106, where it is amplified, for example, 20 times,and applied to the inverting input of an operational amplifier 108. (Theoperational amplifier 106 and the operational amplifier 108 are alsoseen in FIG. 3A where they are designated with a prime (′); however, theinverting and noninverting inputs are switched, as discussed below ingreater detail.) As mentioned, the discharge current limit set by thehost 101 is determined by a host-set digital value established in thedischarge current register 102. The digital value is converted to ananalog value by a D/A converter 104, which is applied to thenoninverting input of the operational amplifier 108.

When the discharge current, I_(DISCHG), creates a voltage across thecharging current sensing resistor 46 that is greater than the analogvoltage established by the value in the discharge current register 102,the output of the operational amplifier 108 begins to follow the voltageproduced by the discharge current, I_(DISCHG). The output voltage isintegrated by the feedback integrator 66, the output of which is appliedto the noninverting input of a comparator 110 (see FIG. 3A). A rampvoltage 109 is applied to the inverting input of the comparator 110.Thus, the output of the comparator 110 is a pulse-width-modulated(PWMed) voltage, the duty cycle of which is determined by the voltagelevel of the output of the feedback integrator 66. This, in turn,controls the driver logic circuit 72 which controls the on and off timesof the boost MOSFET devices 42 and 40 (see FIG. 2), which limit theamount of current drawn from the rechargeable battery pack 22 accordingto the digital value loaded into the discharge current register 102.

When the embodiment of the rechargeable battery pack current regulationcircuit 100 is instantiated in the amplifier, integrator, duty cycle,and driver circuits of FIG. 3A the same circuitry that is used to limitthe charge current may also be utilized to perform the discharge currentlimiting function, through the use of dynamic switching (not shown) ofthe inverting and noninverting inputs. The circuit configuration showingoperational amplifier 106′ and operational amplifier 108′ is shown inFIG. 3A as it would appear to support charge-current limiting. Tosupport discharge-current limiting, the inverting and noninvertinginputs of the amplifier 106′ and operational amplifier 108′ aredynamically switched, for example, when the charger circuit 30 entersboost mode, to the configurations shown in FIG. 4.

Another embodiment of a rechargeable battery pack current regulationcircuit 120 that may be employed is shown in FIG. 5, to which referenceis now additionally made. The battery pack current regulation circuit120 of FIG. 5 can be programmed by an analog voltage that is used to setthe discharging current limit. In one embodiment, the analog voltage canbe established by a reference voltage and a two-resistor divider 122 andin another embodiment from a current source and one resistor (notshown). The analog voltage can be processed by an internal circuit toproduce a desired DC bias voltage that to produce the dischargingcurrent limit reference voltage. The analog voltage may be set, forexample, by a user upon the installation of the rechargeable batterypack 22 having known device characteristics, including the maximumdischarge current.

In operation, the battery pack current regulation circuit 120 senses thedischarge current from the rechargeable battery pack 22 by monitoringthe voltage nodes SRP and SRN on each side of the charging currentsensing resistor 46 (see FIG. 2). As before, in FIG. 5, the current inthe charging current sensing resistor 46 is labeled “I_(DISCHG),” sincethe discharge current is of interest when the charger circuit 30 is inits boost mode of operation and the rechargeable battery pack 22 is usedto supplement the current from the adapter 24 and is thereforedischarging current.

The voltage on the nodes SRP and SRN is applied to the inputs of anoperational amplifier 106, where it is amplified, for example, 20 times,and applied to the inverting input of an operational amplifier 108. (Theoperational amplifier 106 and the operational amplifier 108 are alsoseen in FIG. 3A where they are designated with a prime (′); however, theinverting and noninverting inputs are switched, as discussed below ingreater detail.) As mentioned, the discharge current limit is set by areference voltage, a voltage divider 122 being shown for illustration inFIG. 5. The reference voltage may be amplified, for example eight timesin the embodiment illustrated, by an operational amplifier 124 andapplied to the non-inverting input of the operational amplifier 108.

When the discharge current, I_(DISCHG), creates a voltage across thecharging current sensing resistor 46 that is greater than the analogvoltage established by the reference voltage at the output of theoperational amplifier 124, the output of the operational amplifier 108begins to follow the voltage produced by the discharge current,I_(DISCHG). The output voltage is integrated by the feedback integrator66, the output of which is applied to the noninverting input of anoperational amplifier 110 (FIG. 3A). A ramp voltage 109 is applied tothe inverting input of the comparator 110. Thus, the output of theoperational amplifier 110 is a pulse-width-modulated (PWMed) voltage,the duty cycle of which is determined by the voltage level of the outputof the feedback integrator 66. This, in turn, controls the driver logiccircuit 72 which controls the on and off times of the boost MOSFETdevices 42 and 40 (see FIG. 2), which limit the amount of current drawnfrom the rechargeable battery pack 22, according to the preset referencevoltage.

When the embodiment of the rechargeable battery pack current regulationcircuit 120 is instantiated in the amplifier, integrator, duty cycle,and driver circuits of FIG. 3A the same circuitry that is used to limitthe charge current may also be utilized to perform the discharge currentlimiting function, through the use of dynamic switching (not shown) ofthe inverting and noninverting inputs. The circuit configuration showingoperational amplifier 106′ and operational amplifier 108′ is shown inFIG. 3A as it would appear to support charge-current limiting. Tosupport discharge-current limiting, the inverting and noninvertinginputs of the operational amplifier 106′ and operational amplifier 108′are dynamically switched, for example, when the charger circuit 30enters boost mode, to the configurations shown in FIG. 5.

The digital register embodiment of FIG. 4 and the analog referencevoltage embodiment of FIG. 5 can be used together, wherein the batterydischarge current limit is the lower of these two current limits. Anembodiment of a battery pack current regulation circuit 130 employing adigital register and analog reference voltage to establish the dischargecurrent limit of the rechargeable battery pack 22 is shown in FIG. 6, towhich reference is now additionally made. As with the embodiment shownin FIG. 4 above, the battery pack current regulation circuit 130 of FIG.6 is programmable through the use of a digital register 102 that enablesthe discharging current limit to be set by a host 101, such as asmartphone, notebook, tablet, netbook computing device, or the like, viaa system management bus, an I2C bus, or the like.

The battery pack current regulation circuit 130 of FIG. 6 is alsoprogrammable through the use of an analog voltage, for example, derivedfrom a voltage divider 122, or other voltage source (not shown) in themanner described in FIG. 5 above. The battery pack current regulationcircuit 130 senses the discharge current from the rechargeable batterypack 22 by monitoring the voltage nodes SRP and SRN on each side of thecharging current sensing resistor 46 (see FIG. 2). In FIG. 6, thecurrent in the charging current sensing resistor 46 is labeled“I_(DISCHG),” since the discharge current is of interest when thecharger circuit 30 is in its boost mode of operation and therechargeable battery pack 22 is used to supplement the current from theadapter 24 and is therefore discharging current.

The voltage on the nodes SRP and SRN is applied to the inputs of anoperational amplifier 106, where it is amplified, for example, 20 times,and applied to the inverting input of an operational amplifier 108. Thedischarge current limit set by the host 101 is determined by a host-setdigital value established in the discharge current register 102. Thedigital value is converted to an analog value by a D/A converter 104,which is applied to the inverting input of the operational amplifier108.

The output of the operational amplifier 106 is also applied to theinverting input of an operational amplifier 134, which receives theoutput voltage from the amplifier 124 on its noninverting input. Theoutputs from the operational amplifiers 108 and 134 are connected bydiodes 136 and 138 to the input of the feedback integrator 66, wherebythe lower voltage first initiates the action of the feedback integrator66.

In operation, when the discharge current, _(IDISCHG), creates a voltageacross the charging current sensing resistor 46 that is greater than theanalog voltage established by the value in the discharge currentregister 102, the output of the operational amplifier 108 begins tofollow the voltage produced by the discharge current, _(IDISCHG). Inaddition, when the discharge current, I_(DISCHG), creates a voltageacross the charging current sensing resistor 46 that is greater than theanalog voltage established by the voltage divider 122, the output of theoperational amplifier 134 begins to follow the voltage produced by thedischarge current, _(IDISCHG). The lower of the two voltages initiatesintegration by the feedback integrator 66.

Thus, the output voltage from diodes 136 and 138 is integrated by thefeedback integrator 66, the output of which is applied to thenoninverting input of a comparator 110. A ramp voltage 109 is applied tothe inverting input of the comparator 110. Therefore, the output of thecomparator 110 is a pulse-width-modulated (PWMed) voltage, the dutycycle of which is determined by the voltage level of the output of thefeedback integrator 66. This, in turn, controls the driver logic circuit72 which controls the on and off time of the boost MOSFET device 42 and40 (see FIG. 2), which limits the amount of current drawn from therechargeable battery pack 22, according to the digital value loaded intothe discharge current register 102 or to a preset reference voltage.

When the embodiment of the rechargeable battery pack current regulationcircuit 130 is instantiated in the amplifier, integrator, duty cycle,and driver circuits of FIG. 3A the same circuitry that is used to limitthe charge current may also be utilized to perform the discharge currentlimiting function, through the use of dynamic switching (not shown) ofthe inverting and noninverting inputs and reversal of the output diodes136 and 138. The circuit configuration showing operational amplifiers106′ and 108′, and diodes 136′ and 138′ is shown in FIG. 3A as it wouldappear to support charge-current limiting. To support discharge-currentlimiting, the inverting and noninverting inputs of the operationalamplifiers 106′ and 108′ are dynamically switched and the diodes 136′and 138′ are reversed, for example, when the charger circuit 30 entersboost mode, to match the configurations shown in FIG. 6.

Electrical connections, couplings, and connections have been describedwith respect to various devices or elements. The connections andcouplings may be direct or indirect. A connection between a first andsecond electrical device may be a direct electrical connection or may bean indirect electrical connection. An indirect electrical connection mayinclude interposed elements that may process the signals from the firstelectrical device to the second electrical device.

Although the invention has been described and illustrated with a certaindegree of particularity, it should be understood that the presentdisclosure has been made by way of example only, and that numerouschanges in the combination and arrangement of parts may be resorted towithout departing from the spirit and scope of the invention, ashereinafter claimed.

1. A power supply system, comprising: a rechargeable battery connectableto deliver a supply current to a load; a circuit to limit a dischargecurrent from said rechargeable battery when said rechargeable battery issupplying power to said load.
 2. The power supply system of claim 1further comprising: buck mode circuitry; boost mode circuitry; andswitching circuitry to switch from said buck mode circuitry to saidboost mode circuitry to supply current to said load above apredetermined limit, and wherein said rechargeable battery suppliesadditional current when said boost mode circuitry is switched to supplysaid supply current above said predetermined limit.
 3. The power supplysystem of claim 1 wherein said circuit to limit a discharge currentcomprises: a digital register for containing a digital valuerepresenting a desired discharge current limit; a d/a converter toconvert said digital value to a reference voltage; a circuit to sense adischarge current from said rechargeable battery to produce a dischargevoltage representing said discharge current; and an operationalamplifier to amplify said reference voltage value with said dischargevoltage to produce an output that follows said discharge voltage whensaid discharge voltage is larger than said reference voltage.
 4. Thepower supply system of claim 3 wherein said digital value is establishedby a host computer.
 5. The power supply system of claim 3 furthercomprising: an integrator for integrating said output from saidoperational amplifier; a pulse-width-modulation (PWM) circuit forproducing a control signal having a PWM duty cycle representing saiddischarge voltage; and a driver circuit for delivering said supplycurrent to said load according to said control signal.
 6. The powersupply system of claim 1 wherein said circuit to limit a dischargecurrent comprises: a reference voltage source to produce a referencevoltage; a circuit to sense a discharge current from said rechargeablebattery to produce a discharge voltage representing said dischargecurrent; and an operational amplifier to amplify said reference voltagewith said discharge voltage to produce an output that follows saiddischarge voltage when said discharge voltage is larger than saidreference voltage.
 7. The power supply system of claim 6 wherein saidreference voltage is established by a resistor voltage divider.
 8. Thepower supply system of claim 6 wherein said reference voltage is set bya user.
 9. The power supply system of claim 6 further comprising: anintegrator for integrating said output from said operational amplifier;a pulse-width-modulation (PWM) circuit for producing a control signalhaving a PWM duty cycle representing said discharge voltage; and adriver circuit for delivering said supply current to said load accordingto said control signal.
 10. The power supply system of claim 1 whereinsaid circuit to limit a discharge current comprises: a circuit to sensea discharge current from said rechargeable battery to produce adischarge voltage representing said discharge current; a digitalregister for containing a digital value representing a desired dischargecurrent limit; a d/a converter to convert said digital value to a firstreference voltage; a reference voltage source to produce a secondreference voltage; a first operational amplifier to amplify said firstreference voltage with said discharge voltage to produce a first outputthat follows said discharge voltage when said discharge voltage islarger than said first reference voltage; a second operational amplifierto amplify said second reference voltage with said discharge voltageproduce a second output that follows said discharge voltage when saiddischarge voltage is larger than said second reference voltage; and acircuit to produce a combined voltage from said first and secondoutputs.
 11. The power supply system of claim 10 wherein said digitalvalue is established by a host computer.
 12. The power supply system ofclaim 10 wherein said reference voltage source is adjusted by a user.13. The power supply system of claim 10 further comprising: anintegrator for integrating said combined voltage; apulse-width-modulation (PWM) circuit for receiving said combined voltageand producing a control signal having a PWM duty cycle representing saiddischarge voltage; and a driver circuit for delivering said supplycurrent to said load according to said control signal.
 14. A method foroperating a power supply system, comprising: providing a rechargeablebattery connectable to deliver a supply current to a load; and providinga circuit to limit a discharge current from said rechargeable batterywhen said rechargeable battery is supplying power to said load.
 15. Themethod of claim 14 further comprising switching from a buck mode ofoperation to a boost mode of operation in which said rechargeablebattery supplies additional supply current to said load.
 16. The methodof claim 14 further comprising: when said discharge current exceeds apredetermined limit, generating a control signal having a duty cyclecorresponding to an amount by which discharge current exceeds saidpredetermined limit; and using said control signal to control the supplycurrent to limit said discharge current.
 17. The method of claim 14wherein said providing a circuit to limit a discharge current from saidrechargeable battery when said rechargeable battery is supplying powerto said load comprises providing a digital register containing a digitalvalue set by a host to represent a discharge current limit.
 18. Themethod of claim 17 further comprising converting said digital value toan analog voltage representing said discharge current.
 19. The method ofclaim 14 wherein said providing a circuit to limit a discharge currentfrom said rechargeable battery when said rechargeable battery issupplying power to said load comprises providing a user settablereference voltage to represent a discharge current limit.
 20. The methodof claim 14 wherein said providing a circuit to limit a dischargecurrent from said rechargeable battery when said rechargeable battery issupplying power to said load comprises providing a digital registercontaining a digital value set by a host to represent a first dischargecurrent limit, providing a user settable reference voltage to representa second discharge current limit, and using the lower of said first andsecond discharge current limits to limit said discharge current.